Two-wire, electronic switch

Abstract

Two-wire, electronic switch which performs sensing functions, measurement functions, and output-control functions for an electrical load without receiving power from a power source, external or internal, other than the power source for the electrical load that is controlled by the switch. Electronic components of a two-wire, electronic switch which is fabricated in accordance with the present invention obtain power: (a) when the switch is off, from a power source which drives a load which is controlled by the switch and (b) when the switch is on, from an output of devices which convert current to voltage and which receive at least a portion of a current through the load as input.

What is claimed is: 
     
       1. Power coupling apparatus for coupling power from a power source to a switch, which switch is comprised of (a) two inputs, (b) means for sensing a condition, and (c) means, in response thereto, for causing the switch to be on or off at its inputs, one of the inputs being returned to a load that is being switched and the other of the inputs being returned to the power source, the power source being further connected to the load to supply current to the load whenever the switch is on, the power apparatus comprising: switch-off-power means for coupling power from the power source to the switch whenever the switch is off; and   switch-on-power means for extracting power from the power source and for coupling the extracted power to the switch whenever the switch is on, wherein the switch-on-power means comprises: (a) means for extracting current supplied to the load from the power source, and   (b) supply means, in response to the extracted current, for providing an output voltage which is coupled to the switch wherein the supply means comprises one or more photovoltaic devices.     
     
     
       2. The power coupling apparatus of claim 1 wherein the power source is a DC power source and the switch-on-power means extracts current from the DC power source. 
     
     
       3. The power coupling apparatus of claim 1 wherein the power source is an AC power source and the switch-on-power means extracts current from the AC power source. 
     
     
       4. The power coupling apparatus of claim 1 wherein the power coupling apparatus further comprises means for shunting current around the switch-on-power means. 
     
     
       5. The power coupling apparatus of claim 2 wherein the current shunting means comprises a diode. 
     
     
       6. The power coupling apparatus of claim 1 wherein the one or more photovoltaic devices comprises two or more photovoltaic devices wherein the inputs of at least two of the two or more photovoltaic devices are connected in parallel and the outputs of the at least two of the two or more photovoltaic devices are connected in series. 
     
     
       7. An electronic switch having two inputs, one of the inputs being returned to a load that is controlled by the switch and the other of the inputs being returned to a power source, the power source being further connected to the load to supply current to the load whenever the switch is on, which switch comprises: sensing means for sensing a physical condition;   measuring means, in connection with the sensing means, for providing an output which is a predetermined function of the physical condition;   output-control means, in response to the output from the measuring means, for causing an output means to be on or off, whereby, the switch is caused to be on or off at the inputs;   switch-off-power means for coupling power from the power source to the measuring means and to the output-control means whenever the switch is off; and   switch-on-power means for extracting power from the power source and for coupling the extracted power to the measuring means and to the output-control means whenever the switch is on, wherein the switch-on-power means comprises: (a) means for extracting current supplied to the load from the power source, and   (b) supply means, in response to the extracted current, for providing an output voltage which is coupled to the measuring means and to the output-control means wherein the supply means comprises one or more photovoltaic devices.     
     
     
       8. The electronic switch of claim 7 wherein the switch further comprises means for shunting current around the switch-on-power means. 
     
     
       9. The electronic switch of claim 8 wherein the current shunting means comprises a diode. 
     
     
       10. The electronic switch of claim 7 wherein the output means comprises solid state electronic output means. 
     
     
       11. The electronic switch of claim 10 wherein the solid state electronic output means comprises a MOSFET. 
     
     
       12. The electronic switch of claim 11 wherein the switch-off-power means comprises a diode. 
     
     
       13. The electronic switch of claim 10 wherein: the sensing means comprises a thermistor;   the measuring means comprises a bridge; and   the output-control means comprises a comparator.   
     
     
       14. The electronic switch of claim 7 wherein the one or more photovoltaic devices comprises two or more photovoltaic devices wherein the inputs of at least two of the two or more photovoltaic devices are connected in parallel and the outputs of the at least two of the two or more photovoltaic devices are connected in series. 
     
     
       15. An electronic switch having two inputs, one of the inputs being returned to a load that is controlled by the switch and the other of the inputs being returned to a power source, the power source being further connected to the load to supply current to the load whenever the switch is on, which switch comprises: sensing means for sensing a physical condition;   measuring means, in connection with the sensing means, for providing an output which is a predetermined function of the physical condition;   output-control means, in response to the output from the measuring means, for causing an output means to be on or off, whereby, the switch is caused to be on or off at the inputs;   switch-off-power means, in parallel with the output means, for coupling power from the power source to the measuring means and to the output-control means whenever the switch is off; and   switch-on-power means, in series with the output means, for extracting power from the power source and for coupling the extracted power to the measuring means and to the output-control means whenever the switch is on, wherein the switch-on-power means comprises: (a) means for extracting a portion of current supplied to the load from the power source, and   (b) supply means, in response to the extracted portion of current, for providing an output voltage which is coupled to the measuring means and to the output-control means wherein the supply means comprises one or more photovoltaic devices.     
     
     
       16. The electronic switch of claim 15 wherein: the switch-off-power means comprises a diode and a resistance;   the output means comprises a MOSFET; and   wherein the one or more photovoltaic devices comprises two or more photovoltaic devices wherein the inputs of at least two of the two or more photovoltaic devices are connected in parallel and the outputs of the at least two of the two or more photovoltaic devices are connected in series.